Why are drugs abused? How does drug abuse alter behavior? We here propose a schema describing social and pharmacological factors which may contribute to drug abuse, and social and pharmacological factors which may alter behavior in drug abusers. This heuristic schema leads to 5 hypotheses which we will test: (1) a deprived environment with no social reinforcement will be a stimulus which strengthens a drug habit. (2a) Both pharmacological and social factors can reinforce and maintain drug-taking behaviors. (2b) But over time the pharmacological reinforcement from narcotics will be more potent than social reinforcement in determining behavior. (3a) After drug use social dominance behavior may be increased, both by direct drug effects and by the social behavior of those around the user. (3b) This post-ingestion behavior of others toward a drug-user can reinforce further drug-taking. (4) The chronic use of different drugs will have different effects on general motor activity, work, and social behavior. (5a) Chronic self-administration of narcotics will decrease female sexual behavior. (5b) But when narcotic administration is contingent on female sexual behavior sexual behavior will increase. Because we plan to develop and measure chronic drug habits and drug-related deviant behavior, human subjects would be inappropriate. As in our previous experiments the subjects will be Macaca nemestrina monkeys housed in social groups. The animals will be free-ranging, wearing back-pack injection devices which we are currently developing. The close relationship of physiology and social behavior in man and macaque should make our studies applicable to human research and treatment.